Sensitivity of Biogenic Volatile Organic Compounds Emissions to Leaf Area Index and Land Cover in Beijing

摘要

The Beijing area has suffered from severe air quality pollution in recent years, including ozone pollution in the summer. Except for the anthropogenic emissions inventory, understanding the local ozone pollution still requires the reliable biogenic emission inventory. The forest coverage rate rose from 20.6 % to 35.8 % during 1998–2013 in Beijing according to the National Forest Resource Survey (NFRS). In this study, we established a new high resolution biogenic volatile organic compounds (BVOCs) emission inventory in Beijing based on Model of Emission of Gases and Aerosols from Nature (MEGAN) v2.1 model with three independent leaf area index (LAI) products and three independent land cover products. The Global LAnd Surface Satellite (GLASS) LAI, Moderate-Resolution Imaging Spectroradiometer (MODIS) MCD15 LAI, GEOland (GEO) v2 LAI datasets, and the Finer Resolution Observation and Monitoring of Global Land Cover (FROM-GLC), MODIS MCD12Q1 PFT products and Climate Change Initiative Land Cover (CCI-LC) products are used to design five experiments, as E1-E5, to calculate and test the sensitivity of the model. Based on the meteorological conditions from Weather Forecasting and Research (WRF) model, this inventory is an hourly inventory with 3-km spatial resolution. The result shows: (1) According to the baseline estimation, the total amount of BVOCs emissions are 99.9 Gg for Beijing area. The estimated annual emissions of isoprene, monoterpenes, sesquiterpenes and other VOCs are 52.5 Gg, 11.1 Gg, 1.4 Gg and 34.9 Gg, respectively. (2) The BVOCs emissions have the significant seasonal variability, which the summer season contributes 76.6 % of the total BVOCs emissions in Beijing, and the winter season only contributes 0.3 % emissions due to the low temperature and near-zero biomass of deciduous trees. (3) The broadleaf tree, as the dominant contributor to the BVOCs emissions, accounts for 94.5 % isoprene, 53.3 % monoterpenes, 53.8 % sesquiterpenes and 34.1 % other VOCs. (4) The MODIS LAI lead to a 17.4 % decline in BVOCs emissions because of the large mask area near the urban and water area. However, the GEO and GLASS LAI only led to a 1.0 % difference of total BVOCs emissions even with different temporal updating frequency of LAI. (5) The difference of PFTs have an obvious effect on the spatial distribution and density of BVOCs emissions. The MODIS and CCI-LC land cover led to an approximate 5.0 % and 26.0 % decline in BVOCs emissions compared with the baseline estimation. (6) The estimation of local BVOCs emissions in this study is much higher than the previous studies, and the development of local forest is main reason led to such the difference, thus implying that previous estimation of BVOCs in Beijing is underestimated and is not suitable for the current scene. In addition, further study will investigate and evaluate the effect of BVOCs on the local atmospheric environment through the regional chemistry transport model.